I mounted the gearbox to a 5mm alloy plate. This attaches via set screws to two fairly heavy (20x10mm) stainless steel bars that were tig welded to the frame once assembled on the shaft for alignment (spool removed first). The winch shaft gets modified and the motor shaft made and welded together first. I used a stainless bolt (with the head cut off and a slot so it could be unscrewed and removed later - 5/16 UNF I think it was) screwed into the existing grease nipple thread as an alignment mechanism. The shaft had the corresponding hole drilled right through it to allow removal of the alignment pin and then a thread for a grease nipple tapped into it. The mount for the electrics box is also a 5mm plate secured to the motor mounting plate via a piece of right angle and the gearbox using some plastic spacers I turned up.
Electrics are pretty basic. I didn't bother with a speed control and it only winches up - down is just sorted via the drag. I have used a 100 amp solid state relay from Jaycar with the necessary heat sink and a couple of diodes to protect it from back emf spikes generated when the power is cut. I have fitted two switches in series - one a standard toggle and the other a typical round red emergency stop switch to trigger the relay - should prevent accidental engagement by bumping. I have used commercially made winches with a similar electric set up a few times - just need to keep your concentration so it gets shut off before you pull the rig into the winch. I intend to run at least 30 feet of shock leader so I'll get a fair warning. I also intend to make a boss with a manual handle for a worst case scenario - 4 allen head set screws and the whole electric component slides off the shaft.
The winch is just the standard spigot mount. Col had a rod holder mount made in alloy but it was the wrong angle for my holders so I made one similar out of heavier gauge stainless pipes with a 5mm stainless plate at the junction to allow for diameter differences. The top pipe has a high density poly bush inserted that was turned to fit. I didn't want to make any new holes in the gunwale and the boats rod holders are fully welded ones - stronger than the glass they are in. The gunwale would flex when it was loaded so I made up a 5mm alloy backing plate as large as could be fitted and sika bedded it under the gunwale then fitted set screws through the lot to secure the holder.
After winding the braid on, I decided I wasn't happy with the existing roller set up on the front so made up the new one with a stainless ring and a Ronstan sailing pulley. If this doesn't turn out satisfactory I will probably look at an overhead mounted one but I'm not necessarily keen on the extra leverage it puts on the gunwale.